1. Field of the Invention
This invention pertains to tool holders used with spindles on a milling machine, and more particularly with kits used to measure the amount of tension force exerted by the drawbar mechanism to hold the tool holder on the spindle.
2. Description of the Related Art
Spindles are commonly used with tool holders (also known as arbors) to hold tools or cutting heads on a milling machine. Each spindle typically includes a drawbar assembly and a coupler which securely hold the tool holder. Each tool holder includes a conical-shaped body which is placed inside a complementary-shaped receiving space formed on the drawbar assembly. Attached to the tip of the tool holder is a pull stud which engages a complementary-shaped slot formed on a coupler located inside the drawbar assembly. During use, considerable force is exerted on the pull stud and the sides of the tool holder by the coupler and drawbar assembly, respectively, so that the tool holder does not wobble or move inward and outward. If the force exerted by the coupler or drawbar assembly is inadequate, the tool holder can partially disengage from the spindle thereby causing operator injuries, damage to the tool, diminished cutting head life, damage to the work piece, and inaccurate cuts or bores.
During use, the coupler and drawbar assembly undergo normal wear and tear which gradually reduces its gripping or holding force on the pull stud. Typically, these components must be rebuilt or re-manufactured within a few years depending on the number of uses and the type of work. Generally, re-built or re-manufactured components need repairing or re-manufacturing sooner than new components.
What is needed is a kit that enables operators to accurately and easily measure the coupler and drawbar assembly gripping and holding capacity to determine whether they are operating within factory limits.
It is an object of the present invention to provide a kit designed to be used with the spindle on a milling machine to accurately and easily measure its gripping or holding force.
It is another object of the present invention to provide such a kit that uses mechanical parts sufficiently durable for use in a machine shop environment.
It is a further object of the present invention to provide such a kit that enables the operator to easily calculate the amount of force exerted by the coupler and drawbar assembly on a tool holder to determine if the coupler and drawbar assembly need to be rebuilt or replaced.
These and other objects of the invention that will become apparent are met by a spindle tension testing kit designed to allow mill operators to quickly and easily determine the gripping or holding force of a drawbar assembly on a tool holder. Using the kit, the operator is able to periodically determine whether the coupler and drawbar assembly are operating within factory limits.
The kit includes a force-exerting means that attaches to the distal or second end of a transfer rod that is longitudinally aligned inside the central bore formed on a tool holder. The proximal or first end of the transfer rod is selectively connected to a modified pull stud that is inserted into the drawbar assembly. The end of the modified pull stud is attached to a coupler on the draw bar assembly. The force-exerting means is used to create a pulling force on the transfer rod to test the holding force of the coupler on the modified pull stud. In the first embodiment, the force-exerting means includes an upper frame member that attaches to the second end of the transfer rod, a clevis member, and a pressure gauge. The upper frame member includes a central opening designed to receive the clevis member and a force-exerting means. The clevis member is a U-shaped member that is disposed in an inverted, longitudinally aligned position over a transversely aligned lower member on the upper frame member. When the upper frame member is selectively connected to the transfer rod and the transfer rod is inserted through the central bore formed in the tool holder, the legs on the clevis member extend downward over the lower member on the upper frame member and press against the adjacent end of the tool holder.
The force-exerting means is disposed inside the central opening inside the upper frame member and is used to selectively exert pressure against the clevis member, forcing the legs of the clevis member against the adjacent end of the tool holder. When the tool holder is inserted into the drawbar assembly and the modified pull stud is captured by the coupler, the force-exerting means is selectively operated to gradually exert a separating force between the upper frame member and the clevis member thus pulling the modified pull stud outward from the coupler. By measuring the amount of pressure exerted by the force-exerting means against the clevis member and the upper frame member, the user can determine if the holding force of the coupler on the modified pull stud is within factory limits. In the first embodiment, the force-exerting means is a hydraulically controlled jack with a moving piston capable of measuring and displaying pressure in 100 lbs. per square inch units. The contact surface area of the plunger and the contact surface area of the upper transversely aligned member have areas of surface of one square inch so that the operator may easily measure the tension force in units commonly used by spindle manufacturers.
In a second embodiment, the clevis member and upper frame member are replaced by a sealed measurement unit that includes a piston that moves longitudinally inside a closed cylindrical body. The piston is threadingly connected to the second end of the transfer rod that extends from the distal end of the tool holder. The proximal end of the cylindrical body is placed against the distal end of the tool holder. When the piston is tightened on the transfer rod, the piston is drawn downward into the cylindrical body. A cavity, filled with hydraulic fluid, is formed inside the cylindrical body which expands and compresses as the piston moves inside the cylindrical body. A pressure gauge attached to the cylindrical body measures the hydraulic pressure inside the cavity which informs the user when the desired amount of pulling force exerted on the coupler has been reached. The surface area of the cavity is calibrated to measure in one-square-inch readings.